fuel sender gauge gasket

after owning a 67 Barracuda for 8 years (which I still have) I just picked up 65 as well, very fun to drive!

However after filling up the tank, I found out the gasket on the fuel gauge sending unit is leaking. It looks easy enough to replace, but I've never done it before.

How do I get the retaining ring off, will it just turn? What if it is stuck, any tips to free it up? I have not tried I need to run the full tank mostly empty. It's not leaking too badly.

Any other advice?